The present invention relates to a process using 3-dimensional plotting for producing dental products by which meltable, condensable, thermal or UV or visible light-hardenable unfilled or filled materials are handled by means of a 3-dimensional plotter.
Traditional multiple step molding and casting processes are still overwhelmingly used today for the production of dental replacement products or portions of a dental restoration such as inlays, onlays, bridges, crowns, or prostheses. In this regard, the production of the individual dental form pieces follows in further steps in conventional ways. These conventional processes are proven; however, they require a high degree of effort to produce the finished product. With a view toward ameliorating this effort, a number of processes have been developed, within recent years, with the goal of reducing this effort and improving the quality of the finished products.
In the last several years and, in particular, since 1987, when success was first achieved in generating three dimensional models for a work process directly from a base of computer data, the concept “Rapid Prototyping” has entered the vernacular as a synonym for processes with whose help it is possible to generate, with various accessories or programs, computer data models of varying quality and reliability. In connection with the form or mold free fabrication of items, three dimensional computer pictures are sectioned into layers which are assembled in layer by layer manner, via computer supported fabrication processes, into real three dimensional objects. While the first such models were predominantly demonstration models without any real use potential, models today can, in fact, be fabricated by processes so as to be functional models. Also, small series of items lend themselves to fabrication by these processes. While in the first years of use of such processes, the technically fascinating but cost unfavorable model generating processes predominantly used light hardened acrylic resins (stereolithography), the palette of available materials has clearly grown. Thus, the various processes denominated “Rapid Prototyping” were also implemented in the fabrication of dental products. These principally have comprised selective laser sintering processes, the 3-D printing process, and the stereolithography process.
EP-A-1 021 997 describes the use of a laser sintering process for the fabrication of dental replacement products by which a form body is built of a sinterable powder in a layer by layer manner with each layer being sintered with a laser beam before the application of the following layer. The data needed for controlling the process is data representing the configuration of the form body at each respective layer. An alloy powder in homogeneous form is used as the work material. The disadvantage of this process, however, is that the creation of hollow spaces between the powder material cannot be foreclosed. Moreover, according to the above-noted publication, filled plastic cannot be used as the powder.
WO 97/29901 describes a process (stereolithography) and a device for fabricating three dimensional pieces from a fluid and hardenable medium. In this regard, the piece is built in layer by layer manner with each individual layer being carried off by a laser and thereby hardened. Thereafter, a stripper applies the next layer of the hardenable material and the remaining material is likewise hardened. The publication does not mention the use of materials for dental purposes in its description of the model building process.
U.S. Pat. No. 5,768,134 describes a stereolithographic process for fabricating dental implants. In the disclosed process, a model is generated and modeled in a CAD application; whereby it is known, according to this publication, to use a computer tomography scanned picture for the reconstruction in order to capture the relative position of the prosthetic teeth and the thereunder lying jaw bone and to undertake corrections as needed. As has been noted, this type of process is time consuming while, at the same time, the computer tomography portion is very expensive and is in no way commonly found in dental offices.
There are, moreover, numerous conventional processes by which items can be quickly fabricated based upon models or prototypes. An example of this is described in U.S. Pat. No. 5,370,692. In that disclosed process (modified selective laser sintering), which is heavily weighted toward the replication of bone material in items including thereamong dental implants, the implant layers are built up layer by layer, whereby the application of a layer itself is implemented with a type of pressure on the layer. Ceramic pieces or polymer pieces are preferably bonded with one another in order to build the implant. A pressure application process of this type is, however, not suitable for all circumstances. At the same time, the ceramic cannot, as a rule, be sintered without undergoing a shrinkage process. A further problem in the practical realization of dental prostheses by this process is that a control in the articulator must constantly be performed for the positioning of the tooth. This is accomplished in an intermediate step by the conventional technology involving the creation of a wax prosthesis. It is in practice not possible to remove a model from such a wax prosthesis in a disturbance-free manner since, at the least, micro back cuts occur and a wax model material typically exhibits, even at room temperature, a reduced hardness relative to, for example, plaster.
DE 196 42 247 describes a process for fabricating dental replacement products in which, initially, three dimensional product data is captured and prepared for the fabrication of the dental replacement product. In this process, a computer controlled machine tool is used to ensure the fast production of a prototype based upon the basic product data. Although this process admittedly enables a decidedly exact fabrication of the dental replacement product, the fabrication process requires significant resources and requires an electronically controllable machine tool, which performs the desired work by means of a cutting process. This process suffers from a number of disadvantages, however, in that remnants and debris are created which cannot be tolerated in a dental office practice. Moreover, the thus fabricated dental replacement product must frequently be coated by conventional processes, as the material produced does not meet the aesthetic requirements for such dental replacement products.
It is further conventionally known to use a three dimensional pressure technology for the fast fabrication of prototypes. In this regard, two processes are used: in one process (3-D printing), which has been developed by Massachusetts Institute of Technology, a material in powder form is supplied with a binder material via a spray device in a layer by layer manner to form a shape corresponding to the object to be fabricated and the binder material binds the newly applied powder material to the already applied layers. In this process, the excess non-bound powder material is removed in the finishing of the object. The use of powder material provides design freedom in fabricating an object by this process, whereby nonetheless the object is frequently left with a gritty or granular surface and hollow spaces, which can impact the firmness of the object, cannot be precluded. Follow up handling is typically required to increase the mechanical integrity and the outer surface of the object. In another conventional process (fused deposition modeling), a three dimensional pressure technology is used in connection with electrostatic ink spray nozzles to apply a material hardenable by contact with air. This material is melted and then flowed through the nozzles to be applied thereby. Due to the need to effect a complete through hardening of the material, it is necessary to use significantly small material pieces, whereby the fabrication process takes a correspondingly long time. Typically, a material cord is melted in a 3-D dimensionable nozzle and applied thereby. In this regard, however, the choice of suitable materials is limited to only a few thermoplastic materials such as, for example, ABS. A further disadvantage is that a cord of suitable dimension of the material to be applied must first be produced which can then be subsequently applied through the nozzle.
It is further known to fabricate computer supported three dimensional objects, whereby the three dimensional structure is constructed in layer by layer manner by the addition of micro points or micro cords in a fluid medium (Macromolecular Materials and Engineering 2000, 282, pages 17-21). By this process, it is possible to construct structures from mechanically unstable materials, which, in compensating for gravity by passage in the fluid medium, maintain their geometry after the build up of the structure up to mechanical or chemical consolidation. This process allows in this manner the use of materials, which were heretofore not suitable for a Rapid Prototyping process. The use of this process for the fabrication of dental products is, however, not described in the prior art.